The present invention relates to telephony in general, and in particular to apparatus and methods for transferring a high-speed voice-band data modem signal over telephone networks that incorporate equipment such as multiplexers and pair gain apparatus between the central office and the subscriber.
Digital data is typically transmitted between the central office (CO) and the subscriber by converting the data to analog form suitable for band-pass transmission over POTS lines. Since all modern CO switches are digital, they perform a digital to analog (D/A) conversion on downstream data transmitted to the subscriber and analog to digital (A/D) conversion on upstream data received from the subscriber.
Transmission equipment such as multiplexers or pair gain devices installed between the CO and the subscriber usually require at least two additional conversions per one-way transmission. In a downstream transmission an A/D conversion is performed on transmissions received from the CO, typically at a central office terminal (COT), and a D/A conversion is performed on transmissions to the subscriber, typically at a remote terminal (RT). Upstream transmissions likewise usually require at least two additional conversions.
These additional conversions often degrade the transmission line quality thereby interfering with the operation of high-speed modems such as 56k pulse amplitude modulation modems such that it is often impossible to transmit data above 28,800 Kbps where such transmission equipment is used.
The present invention seeks to provide novel apparatus and methods for transferring a high-speed voice-band data modem signal over telephone networks that incorporate equipment such as multiplexers and pair gain apparatus between the central office and the subscriber, or other DAML-type systems. The present invention provides an improved system which overcomes the known disadvantages of the prior art as discussed above and provides transmission throughput substantially at the rated symbol rates of 56k pulse amplitude modulation modems.
There is thus provided in accordance with a preferred embodiment of the present invention a telecommunications system including an at least partially digital telephone link having an analog end portion, first and second modems disposed along the link, and analog/digital devices disposed along the link intermediate the modems which are operative to support communications between the first and second modems substantially at bit rates in excess of 28.8 Kbps.
Further in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the modems, the analog signal having been prepared at a first codec, a clock interface operative to receive clock timing information of the first codec, a second codec operative to convert the analog signal for digital transmission, digital transmission apparatus operative to digitally transmit the converted signal and the clock timing information, a digital signal interface operative to receive the converted signal and the clock timing information, and a third codec operative to reconvert the converted signal to an analog form, characterized in that the third codec is operative to reconvert in clock-synchronicity with the first codec in accordance with the clock timing information.
Still further in accordance with a preferred embodiment of the present invention the second and third codecs are operative to perform linear conversion.
Additionally in accordance with a preferred embodiment of the present invention the second and third codecs are operative to perform xcexc-Law companding.
Moreover in accordance with a preferred embodiment of the present invention the second and third codecs are operative to perform a-Law companding.
Further in accordance with a preferred embodiment of the present invention the second and third codecs are operative to perform sampling at a clock rate greater than the clock rate used by the first codec.
Still further in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the modems, a first codec operative to convert the analog signal for digital transmission, digital transmission apparatus operative to digitally transmit the converted signal, a digital signal interface operative to receive the converted signal, and a second codec operative to reconvert the converted signal to an analog form, characterized in that the first codec is operative to convert using linear conversion at a bit resolution greater than the bit resolution of the analog signal, and the second codec is operative to reconvert using linear conversion.
Additionally in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the modems, the analog signal having been prepared at a first codec, and a second codec operative to convert the analog signal for digital transmission, characterized in that the second codec is operative to sample the analog signal at a clock rate greater than the clock rate used by the first codec.
Moreover in accordance with a preferred embodiment of the present invention the system further includes digital transmission apparatus operative to digitally transmit the converted signal, a digital signal interface operative to receive the converted signal, and a third codec operative to reconvert the converted signal to an analog form.
Further in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the first and second modems, a codec and a third modem, both arranged to receive the analog signal in parallel, a processor operative to receive digitized data from the third modem and provide the digitized data to a fourth modem, a selector operative to receive digitized data from either of the codec and the fourth modem, and digital transmission apparatus operative to digitally transmit the digitized data received from the selector, the selector selectively provides the digitized data to the digital transmission apparatus based on at least one predefined selection criterion.
Still further in accordance with a preferred embodiment of the present invention the selector is operative to selectively provide either of the digitized data received from the codec based on the absence of a modem training signal received at the third modem, and the digitized data received from the fourth modem based on the detection of a modem training signal received at the third modem.
Additionally in accordance with a preferred embodiment of the present invention the system further includes a buffer operative to buffer the digital data received from the third modem.
Moreover in accordance with a preferred embodiment of the present invention the processor is operative to operate both of the third and fourth modems at the same connection speed.
Further in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the modems, a first codec operative to convert the analog signal to digital data form, a DSP filter operative to filter the digital data, digital transmission apparatus operative to digitally transmit the filtered signal, a digital signal interface operative to receive the filtered signal, and a second codec operative to reconvert the filtered signal to an analog form, characterized in that the DSP filter is operative to filter sufficiently to compensate for a combined frequency response between the converting and reconverting steps such that the frequency response is flatter and has a wider passband than the frequency response shown in FIG. 5.
Still further in accordance with a preferred embodiment of the present invention the system further includes a first digital signal interface operative to receive a digital signal representation of digital data from a transmission source associated with one of the modems and extract clock timing information from the digital signal, digital transmission apparatus operative to digitally transmit the digital signal and the clock timing information, a second digital signal interface operative to receive the digital signal and the clock timing information, and a codec operative to convert the digital signal to an analog form, characterized in that the codec converts in clock-synchronicity in accordance with the clock timing information.
Additionally in accordance with a preferred embodiment of the present invention the codec converts using a synchronous low jitter sampling clock.
There is also provided in accordance with a preferred embodiment of the present invention a telecommunications method including providing an at least partially digital telephone link having an analog end portion, disposing first and second modems along the link, and operating analog/digital devices along the link intermediate the modems to support communications between the first and second modems substantially at bit rates in excess of 28.8 Kbps.
There is al so provided in accordance with a preferred embodiment of the present invention a telecommunications method including receiving an analog signal representation of digital data from a transmission source, converting the analog signal for digital transmission, digitally transmitting the converted signal, receiving the converted signal, and reconverting the converted signal to an analog form, characterized in that the converting step includes converting using linear conversion at a bit resolution greater than or equal to the bit resolution of the analog signal, and the reconverting step reconverts using linear conversion.
There is also provided in accordance with a preferred embodiment of the present invention a telecommunications method including receiving an analog signal representation of digital data from a transmission source, the analog signal having been prepared at a first codec, and converting the analog signal for digital transmission, characterized in that the converting step includes sampling the analog signal at a clock rate greater than the clock rate used by the first. codec.
Further in accordance with a preferred embodiment of the present invention both of the clock rates exceed 8 kilohertz.
Still further in accordance with a preferred embodiment of the present invention the method further includes digitally transmitting the converted signal, receiving the converted signal, and reconverting the converted signal to an analog form.
There is also provided in accordance with a preferred embodiment of the present invention a telecommunications method including receiving an analog signal representation of digital data from a transmission source, providing the analog signal to either of a codec and a first modem, providing a processor operative to receive digitized data from the first modem and provide the digitized data to a second modem, providing a selector operative to receive digitized data from either of the codec and the second modem, and selectively digitally transmitting the digitized data received from one of the codec and the second modem based on at least one predefined selection criterion.
Further in accordance with a preferred embodiment of the present invention the selectively digitally transmitting step includes selectively digitally transmitting the digitized data received from the codec based on the absence of a modem training signal received at the first modem and selectively digitally transmitting the digitized data received from the second modem based on the detection of a modem training signal received at the first modem.
Still further in accordance with a preferred embodiment of the present invention the method further includes buffering the digital data received from the first modem.
Additionally in accordance with a preferred embodiment of the present invention the method further includes operating both of the modems at the same connection speed.
There is also provided in accordance with a preferred embodiment of the present invention a telecommunications method including receiving an analog signal representation of digital data from a transmission source, converting the analog signal to digital data form, DSP-filtering the digital data, digitally transmitting the filtered signal, receiving the filtered signal, and reconverting the filtered signal to an analog form, characterized in that the DSP-filtering step includes filtering to sufficiently compensate for a combined frequency response between the converting and reconverting steps such that the frequency response is flatter and has a wider passband than the frequency response shown in FIG. 5.
There is also provided in accordance with a preferred embodiment of the present invention a telecommunications method including (a) receiving a digital signal representation of digital data from a digital transmission source, (b) extracting clock timing information from the digital signal, (c) digitally transmitting the digital signal and the clock timing information, (d) receiving the digital signal and the clock timing information, and (e) converting the digital signal to an analog form, characterized in that the converting step (e) includes converting at a codec that is in clock-synchronicity in accordance with the clock timing information.
Further in accordance with a preferred embodiment of the present invention the method further includes prior to the receiving step (a) (f) receiving an analog signal representation of the digital data of the receiving step (a) from an analog transmission source, the analog signal having been prepared at a first codec, (g) receiving clock timing information of the first codec, (h) converting the analog signal into the digital signal representation of the digital data of the receiving step (a) for digital transmission, and (i) digitally transmitting the converted signal and the clock timing information.
Still further in accordance with a preferred embodiment of the present invention the converting step (h) includes converting using linear conversion.
Additionally in accordance with a preferred embodiment of the present invention the converting step (h) includes converting using xcexc-Law companding.
Moreover in accordance with a preferred embodiment of the present invention the converting step (h) includes converting using a-Law companding.
Further in accordance with a preferred embodiment of the present invention the converting step (h) includes sampling at a clock rate greater than the clock rate used by the first codec.
Still further in accordance with a preferred embodiment of the present invention the converting step (e) includes converting using a synchronous low jitter sampling clock.
There is also provided in accordance with a preferred embodiment of the present invention a telecommunications system including an analog signal interface operative to receive an analog signal representation of digital data from a transmission source, a first codec operative to convert the analog signal for digital transmission, digital transmission apparatus operative to digitally transmit the converted signal, a digital signal interface operative to receive the converted signal, and a second codec operative to reconvert the converted signal to an analog form, characterized in that the first codec is operative to convert using linear conversion at a bit resolution greater than the bit resolution of the analog signal, and the second codec is operative to reconvert using linear conversion.
Further in accordance with a preferred embodiment of the present invention the codecs operate at a resolution of at least 12 bits.
Still further in accordance with a preferred embodiment of the present invention the codecs operate at a resolution more than 12 bits.
Additionally in accordance with a preferred embodiment of the present invention the codecs operate at a resolution of 16 bits.
Moreover in accordance with a preferred embodiment of the present invention the codecs are operative to perform xcexc-Law companding.
Further in accordance with a preferred embodiment of the present invention the codecs are operative to perform a-Law companding.
There is also provided in accordance with a preferred embodiment of the present invention telecommunications apparatus including an analog signal interface operative to receive an analog signal representation of digital data from a transmission source, the analog signal having been prepared at a first codec, and a second codec operative to convert the analog signal for digital transmission, characterized in that the second codec is operative to sample the analog signal at a clock rate greater than the clock rate used by the first codec.
Further in accordance with a preferred embodiment of the present invention the codecs operate at a sampling rate exceeding 8 kilohertz.
Still further in accordance with a preferred embodiment of the present invention the codecs are operative to perform linear conversion.
Additionally in accordance with a preferred embodiment of the present invention the codecs are operative to perform xcexc-Law companding.
Moreover in accordance with a preferred embodiment of the present invention the codecs are operative to perform a-Law companding.
Further in accordance with a preferred embodiment of the present invention digital transmission apparatus is further included operative to digitally transmit the converted signal, a digital signal interface operative to receive the converted signal, and a third codec operative to reconvert the converted signal to an analog form.
There is also provided in accordance with a preferred embodiment of the present invention Telecommunications apparatus including an analog signal interface operative to receive an analog signal representation of digital data from a transmission source, a codec and a first modem, both arranged to receive the analog signal in parallel, a processor operative to receive digitized data from the first modem and provide the digitized data to a second modem, a selector operative to receive digitized data from either of the codec and the second modem, and digital transmission apparatus operative to digitally transmit the digitized data received from the selector, the selector selectively provides the digitized data to the digital transmission apparatus based on at least one predefined selection criterion.
Further in accordance with a preferred embodiment of the present invention the selector is operative to selectively provide either of the digitized data received from the codec based on the absence of a modem training signal received at the first modem, and the digitized data received from the second modem based on the detection of a modem training signal received at the first modem.
Still further in accordance with a preferred embodiment of the present invention a buffer is further included operative to buffer the digital data received from the first modem.
Additionally in accordance with a preferred embodiment of the present invention the processor is operative to operate both of the modems at the same connection speed.
There is also provided in accordance with a preferred embodiment of the present invention a telecommunications system including an analog signal interface operative to receive an analog signal representation of digital data from a transmission source, a first codec operative to convert the analog signal to digital data form, a DSP filter operative to filter the digital data, digital transmission apparatus operative to digitally transmit the filtered signal, a digital signal interface operative to receive the filtered signal, and a second codec operative to reconvert the filtered signal to an analog form, characterized in that the DSP filter is operative to filter sufficiently to compensate for a combined frequency response of the digital transmission such that the frequency response is flatter and has a wider passband than the frequency response shown in FIG. 5.
There is also provided in accordance with a preferred embodiment of the present invention a telecommunications system including a first digital signal interface operative to receive a digital signal representation of digital data from a digital transmission source and extract clock timing information from the digital signal, digital transmission apparatus operative to digitally transmit the digital signal and the clock timing information, a second digital signal interface operative to receive the digital signal and the clock timing information, and a third codec operative to convert the digital signal to an analog form, characterized in that the third codec converts in clock-synchronicity in accordance with the clock timing information.
Further in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of the digital data from an analog transmission source, the analog signal having been prepared at a first codec, a clock interface operative to receive clock timing information of the first codec, a second codec operative to convert the analog signal for digital transmission, and digital transmission apparatus operative to digitally transmit the converted signal and the clock timing information.
Still further in accordance with a preferred embodiment of the present invention the codec is operative to perform linear conversion.
Additionally in accordance with a preferred embodiment of the present invention the codec is operative to perform xcexc-Law companding.
Moreover in accordance with a preferred embodiment of the present invention the codec is operative to perform a-Law companding.
Further in accordance with a preferred embodiment of the present invention the codec is operative to perform sampling at a clock rate greater than the clock rate used to prepare the digital signal representation of digital data.
Still further in accordance with a preferred embodiment of the present invention the codec converts using a synchronous low jitter sampling clock.
There is also provided in accordance with a preferred embodiment of the present invention Telecommunications apparatus including an analog signal interface operative to receive an analog signal representation of digital data from a transmission source, a first codec operative to convert the analog signal for digital transmission, and digital transmission apparatus operative to digitally transmit the converted signal, characterized in that the first codec is operative to convert using linear conversion at a bit resolution greater than the bit resolution of the analog signal.
There is also provided in accordance with a preferred embodiment of the present invention Telecommunications apparatus including a digital signal interface operative to receive a digital signal representation of an analog signal representation of digital data from a transmission source, the digital signal representation having been converted using linear conversion at a bit resolution greater than or equal to the bit resolution of the analog signal, and a codec operative to reconvert the converted signal to an analog form using linear conversion.
There is also provided in accordance with a preferred embodiment of the present invention Telecommunications apparatus including an analog signal interface operative to receive an analog signal representation of digital data from a transmission source, a codec operative to convert the analog signal to digital data form, a DSP filter operative to filter the digital data, and digital transmission apparatus operative to digitally transmit the filtered signal, characterized in that the DSP filter is operative to filter sufficiently to compensate for a combined frequency response of the digital transmission such that the frequency response is flatter and has a wider passband than the frequency response shown in FIG. 5.
It is noted that throughout the specification and claims the terms xe2x80x9cend-userxe2x80x9d and xe2x80x9csubscriberxe2x80x9d are used interchangeably. It is also noted that throughout the specification and claims the terms xe2x80x9clocal exchangexe2x80x9d and xe2x80x9ccentral officexe2x80x9d are used interchangeably. It is also noted that throughout the specification and claims the terms xe2x80x9cCODECxe2x80x9d and xe2x80x9canalog/digital devicexe2x80x9d are used interchangeably.